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Heavy versus Light wheels - Acceleration Tests and their results
- Thread starter MvM
- Start date
The Non-US or UK NSX has of course a metric scale for the speedometer. Normally they read up to 280 km/hour but since my personal NSX is So Extremely Fast, it needed a 320 km/hour speedo
:smile: You know, so that all those little kids peering into the car when it is parked will be even more impressed.
GoldNSX said:
I was talking about the ratio between the weight of the wheels+tires and the rest of the car.
So, a 150 lbs guy trying to move a larger object is moving a
150 x 15.27 = 2290 lbs (if the ratio is that of a NSX versus BBS wheels)
150 x 17.93 = 2690 lbs (if the ratio is that of a NSX versus OZ wheels)
And yes, of course the guy is moving himself as well of course.
Hi Rene, I might take you up on that offer. Then we can answer than question as well.
Thanks for sharing your valuable time to conduct this test (any chance you can submit this article for the next issue of the NSXDRIVER magazine)?
Hmm, there's an idea
But it might be more interesting if I would have a little more data to publish.
Like redo the tests with the 16/17 wheels as Rsevo already suggested.
Or perhaps the influence of the difference ECU's available at the moment for NA-NSX's (OEM, Dali, SOS, ProSpeed). Things like that.
Your point is very important and for a race multiply times 15 or 30 or more and you get 7 seconds and 15 seconds.
The other important factor is wheel dimension which smaller increases the effective torque giving you better/stronger acceleration for the track
If we add in the human factor - shifting - which I think can add greater positive or negative perfomance than the wheel replacement and driving skill well you know where I am going......
We should all - most all - should accept the fact that we are looking for a cosmetic improvement rather than perfromace improvement when we replace wheels. Sorry if that's already a given and I missed the point :redface:
If you want performace.....Invest in some driving schools!
Gotta get back to my "Tire Rack" page and see which 18/19 package will give me the best performance :biggrin:
Thank you for taking the time to conduct this test. I was thinking that my GT-Cs might be penalizing me on acceleration but after reading your results, I am going to stick with them.
I agree that repeating the test with stock wheels has merit. I also like the idea of testing different performance chips.
I agree that repeating the test with stock wheels has merit. I also like the idea of testing different performance chips.
Nice job, it's good to have data. It's very hard to get good repeatability on the road. A chassis dyno would be ideal for the comparison, for several reasons.
First, obviously wind gusts and direction will affect the aero drag, and add variability. The Cd*A (aero drag force) is very much dependent on the wind angle (wind direction from vehicle centerline). It would have been best to run multiple "paired" back-back runs, in opposite directions, to cancel the wind speed and direction effects. Auto manufacturers have run these tests in the early morning, or at night when the winds are calm, and less than 5 mpg, and no gusts.
Next, paired tests in opposite direction also tends to cancel road grade effects (there is no such thing as a perfectly flat road, increases variability).
Tire slip is an important variable for accel measurements, and difficult to control. There is an sae procedure that addresses this test, and it's also used by Car and Driver for their road tests (they run from a standing start). Again, a chassis dyno would have made it more repeatable (could ballast the car to minimize slip, run in a higher gear as well, and no wind and grade variability).
Not sure about your meter, and it's repeatability/accurcy (no comment).
Overall kudos for taking the time to run this. Itshows the importance of keeping oems and aftermarket parts people honest, which is why there are sae, eec (euro) and jsae (japan) standards for these tests.
Thanks for your compliment.
I could have done a dyno, but that still would not have told me anything about the real-life results under acceleration.
The actual tests were done in opposite directions. After doing one run, I truned around the car, reset the AP22 and then proceeded to do the test in the opposite direction. Maybe I should have stated that a more clearly in the procedure description. As for wind, there was practically no wind to speak off during that test (luckily, because it was cold enough as it was).
As for the accuracy of the AP22, I cannot answer that. The specifications claim that it is accurate to 0.01 G.
I assume that the accuracy of the timing unit is indeed in order of 0.01 seconds. Not sure, but I think it is very probable to think that by now, in 2007, with digitally controlled timing units being used in anything from wristwatches, computers, micro-waves, phones etc. to whatever you can think of, the error of timing in a period of just 5-10seconds is almost unmeasurable small and absolutely not significant considering the other variables.
Good information.
Light or heavy wheels dont make big difference in low speed acceleration, maybe more noticable at higher speed acceleration over 180 km/h?
Did you tested that too?
Cornering and car handling should be generally better with lighter wheels,
isnt it?
Light or heavy wheels dont make big difference in low speed acceleration, maybe more noticable at higher speed acceleration over 180 km/h?
Did you tested that too?
Cornering and car handling should be generally better with lighter wheels,
isnt it?
Handling of the car definately is normally improved with lighter wheels & tires, all other factors being equal of course.
As for the effect of the wheels at higher speeds, I disagree. At higher speeds, you are going to be in a much higher gear so the available torque available for acceleration is much less.
Put perhaps you actually mean taking a larger time interval for the measurement as already suggested. If the timing interval would have been something like 15 seconds instead of just 5, any differences might have been more noticable.
Perhaps I should have taken a Toyote Prius or something for the test. Using a car that's doing 20 to 100 kph is just 5.6 seconds instead of 15 might have helped. But then again, I would have needed a much longer stretch of road of course. As well as more time. AND it would have been less fun to do it.
Wow, again, more real science on an Internet thread. Very nice.
To GoldNSXes points about variability and how testing over a longer period is valuable, and in theroy, this is quite true and is certainly fact. However, in a real world, many variable test, with very small change in test results, eliminating variables and/or magnifiying the effect of the product/item/change will help tell if there is a change. But, I'm done arguing that and I do agree with what you said.
In this test case, there are more variables in my opinion than there are in your opinion, from the sound of it. We had a fair degree of variance in our test results. I say fair degree, compared to how my car performs on a dyno. I get very similar runs (to 1 or 2 hp variance) per dyno run.
2 / 255 = .78% difference
In his tests, he had a .3 second difference on a test that took, at max, 5.88 seconds.
.3 / 5.88 = 5.1% difference
That's a big difference compare to more controlled situations. That is why I was stuck on the point to reduce test windows - to help eliminate this variance.
Now, to MvM's point, you got your independent variables mixed up. The independent variable is the power of the engine (through a driveline including the mass of the wheels). The dependent variable, in this case, was the acceleration of the vehicle.
The wheels don't power the car. The engine does. The wheels must be accelerated, both linearly and rotationally, so their inertia resists this acceleration. But, the mass of the wheel does not provide a force for acceleration like the mass of a person does.
Ok, we are getting very close to about all that can be said on this subject. Which is good as we did stick mostly to real science. I think we can say that there were some variables that were not controlled and they caused the test results to be greater than the difference observed between wheels.
To improve our chances to measure the certainly real changes, however small, we need to reduce these variables or make the effect more significant. One way is to use 1st gear - it will give any change 78% more magnatude. It may also introduce other variables like the possibility of wheel spin.
Another way may be to use a dyno. However, I didn't mention this before as I don't know if an NSX can spin its tires on a dyno in 1st, but I suspect it can.
Also, it may be possible to use a more accurate accelerometer... although I don't know their expected consistency over runs like this.
This continues to be a great subject. I would still like to know how much of a difference lighter wheels make, however small.
To GoldNSXes points about variability and how testing over a longer period is valuable, and in theroy, this is quite true and is certainly fact. However, in a real world, many variable test, with very small change in test results, eliminating variables and/or magnifiying the effect of the product/item/change will help tell if there is a change. But, I'm done arguing that and I do agree with what you said.
In this test case, there are more variables in my opinion than there are in your opinion, from the sound of it. We had a fair degree of variance in our test results. I say fair degree, compared to how my car performs on a dyno. I get very similar runs (to 1 or 2 hp variance) per dyno run.
2 / 255 = .78% difference
In his tests, he had a .3 second difference on a test that took, at max, 5.88 seconds.
.3 / 5.88 = 5.1% difference
That's a big difference compare to more controlled situations. That is why I was stuck on the point to reduce test windows - to help eliminate this variance.
Now, to MvM's point, you got your independent variables mixed up. The independent variable is the power of the engine (through a driveline including the mass of the wheels). The dependent variable, in this case, was the acceleration of the vehicle.
The wheels don't power the car. The engine does. The wheels must be accelerated, both linearly and rotationally, so their inertia resists this acceleration. But, the mass of the wheel does not provide a force for acceleration like the mass of a person does.
Ok, we are getting very close to about all that can be said on this subject. Which is good as we did stick mostly to real science. I think we can say that there were some variables that were not controlled and they caused the test results to be greater than the difference observed between wheels.
To improve our chances to measure the certainly real changes, however small, we need to reduce these variables or make the effect more significant. One way is to use 1st gear - it will give any change 78% more magnatude. It may also introduce other variables like the possibility of wheel spin.
Another way may be to use a dyno. However, I didn't mention this before as I don't know if an NSX can spin its tires on a dyno in 1st, but I suspect it can.
Also, it may be possible to use a more accurate accelerometer... although I don't know their expected consistency over runs like this.
This continues to be a great subject. I would still like to know how much of a difference lighter wheels make, however small.
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+1
Rarely found, I know. For those getting bored please remind the vette owner's 'direct exhaust injection'? I agree with you that the testing window has to be as small as possible to minimize disturbing error variance but not at the cost of only getting half or none of the effect. This would be like omissing variables and this is a big NONO in empirical statistic analysis. MvM's recalculation points to this problem. On the other hand we could minimize the test to a laboratory testing situation (isolating errorous variables) and this would be very interesting but it's simply too expensive AND may not be very realistic depending on how it is done.
The std. dev. of 0.06 and 0.11 have been very small for an empirical test IMO. I agree with you that a dyno has less variance BUT I would not test the wheel weight effect with a dyno because the mass of the car is not moved and you only get the effect of the rear wheels. Our dynos here in Europe are far less quick than the ones in the US. One run takes about 40 sec. from 2-8k in 3rd gear and this is far less then if you accelerate the car on the road. So the acceleration of the wheel is very small and you get near to none effect. Actually the wheel acceleration is kept low as a dyno is intended to measure the engine output without being disturbed by unwanted variables (wheel weight in the case of a dyno).
Fully agree.
Fully agree.
Let's do a summary of all the variables:
Dependent variable: acceleration time
Inpendent variables (only the ones that strongly influence the dependent variable or produce disturbing error variance). Which ones are most important?
- drivers technic (+-constant)
- car (was the same = variable held constant)
- vehicle mass (constant)
- tires (constant)
- tire pressure (I guess it was constant)
- fuel, was the same
- weather (temp. within 2-3 degrees, humidity, athmos. pressure, wind?)
- road (not constant! Of course it has been the same road but you don't drive the exactly same line or begin to accelerate at exactly the same point and hit every small bump at a different speed. Moreover error variance has been introduced by not driving on it always in the same direction. My test above should be a paired one, one for driving A-B and one for B-A (paired sample))
- wheel weight
Please feel free to add your independant var. on the list.
The AP-22 is an quite accurate meter. Of course you could do slightly better but at what costs?
From the list I guess there are only a few indep. var. that resulted in the already low error variance:
- temp. maybe but by how much?
- driver technic but by how much? I guess it's very low.
- ROAD! I think here lies the main cause of the (again even small) error variance.
Hypothesis:
The heavier wheels had a bigger variance than the lighter ones. Why? My hypothesis goes like this: Like I've argued in my 'audiophile' post above the heavier wheels have more problems to transmit the power to the (not perfectly flat) road and therefore are more prone to show one run a good time and the next run a bad time. You won't recognize this as wheel-spin or even reaction of the TCS as this happens only for a fraction of a second and by a small amount. It would have been interesting to see more insight into the higher std. deviation of the heavier wheels.
If this is the case we have measured two effects:
1. influence of lighter wheels on acceleration times on perfectly flat roads
+
2. influence of lighter wheels on the traction of the tires and therefore the influence on the acceleration times
In the test above we've measured both as a 'bundle'. We can't tell them from each other.
Or practically spoken: Do we have to? I'd say NO because we're interested in the acceleration times. That's why I'm not with isolated testing.
I'm feeling that there are more independent variables we can't isolate with on-road G-meter testing.
I think a fair question is - what is the variability of an average stock NSX engine, per pull, from 2k to 8k rpm, on a dyno, in controlled conditions?
Then, what is MvM's engine's variability in the same test case? Is the test engine fairly predictable or does it vary more or less than nomral engines?
Similarly, how does MvM's car vary in on-road tests? Does variability increase?
How reliable is the G-meter?
Of course, 2-3 degrees C is a chunk and humidity and pressure were not recorded. Cooler means more power, but humidity or pressure changes could have counteracted this, but to what extent?
Looking into all the variability we identified, does this amount obfuscate all expected test case variations? I'd hope not, but maybe they do.
I really don't mean to get the last word in on this, so I'm sorry for actually posting this. If you reply on the G-meter and real-world test cases, I'll not reply so we can actually let this end. Thanks for the discussion in any event.
Ok, that's done. Now, can we do the following analysis? Can we consider the torque of the engine, through the gearing, and ultimately the power spent accelerating the vehicle thourgh our test case?
Then, can we determine how much of that torque or power was required to accelerate just the rear wheels over the previously identified acceleration curve? We'd probably need to know the total weight of the rear wheels and tires plus their polar moment of inertia.
Can we then compare the effort required to accelerate the entire vehicle versus that required just to accelerate the wheels? This would give us a percent of effort committed to just rear wheel and tire acceleration.
From here, we can calculate the acceleration of a fictional vehicle, one where the rear wheels and tires have zero mass. This would be the "fastest possible accelerating wheels". (Someone should market these!)
Then, we could extrapolate from the times for the stock weight wheels down to the zero weight wheels and have a very good estimate of how fast a particular weight wheel would help or hurt acceleration.
Anyone think we have enough info to take a stab at it this way?
I think a fair question is - what is the variability of an average stock NSX engine, per pull, from 2k to 8k rpm, on a dyno, in controlled conditions?
Then, what is MvM's engine's variability in the same test case? Is the test engine fairly predictable or does it vary more or less than nomral engines?
Similarly, how does MvM's car vary in on-road tests? Does variability increase?
How reliable is the G-meter?
Of course, 2-3 degrees C is a chunk and humidity and pressure were not recorded. Cooler means more power, but humidity or pressure changes could have counteracted this, but to what extent?
Looking into all the variability we identified, does this amount obfuscate all expected test case variations? I'd hope not, but maybe they do.
I really don't mean to get the last word in on this, so I'm sorry for actually posting this. If you reply on the G-meter and real-world test cases, I'll not reply so we can actually let this end. Thanks for the discussion in any event.
Ok, that's done. Now, can we do the following analysis? Can we consider the torque of the engine, through the gearing, and ultimately the power spent accelerating the vehicle thourgh our test case?
Then, can we determine how much of that torque or power was required to accelerate just the rear wheels over the previously identified acceleration curve? We'd probably need to know the total weight of the rear wheels and tires plus their polar moment of inertia.
Can we then compare the effort required to accelerate the entire vehicle versus that required just to accelerate the wheels? This would give us a percent of effort committed to just rear wheel and tire acceleration.
From here, we can calculate the acceleration of a fictional vehicle, one where the rear wheels and tires have zero mass. This would be the "fastest possible accelerating wheels". (Someone should market these!)
Then, we could extrapolate from the times for the stock weight wheels down to the zero weight wheels and have a very good estimate of how fast a particular weight wheel would help or hurt acceleration.
Anyone think we have enough info to take a stab at it this way?
I agree with most of what you and GoldNSX are saying.
The problem is, however, that in most cases, the answer to the question is simply "We don't know".
Variability of the engine? Don't know. But what we do know is that comparing the dynoes of most NSX's that we have seen dynographs from here on NSXPrime, most runs will show a variance of about 4 HP MAXIMUM over 3 runs. On an engine with about 270 RWHP that's close to 1.5%.
Being only halfway in your max. output during a run, that variance is only increased.
How reliable is the G-meter? Good question, again, same answer. Looking at all the other variables, I would think that the reliability of the AP22 is probably the least of our worries.
Influence of the colder temperature. No idea. At only 30 kph, with an engine only making part of its max. output, probably very small, but still an unknown factor.
Of course, a real life test will have more variables than a much more controlled laboratory test. But the latter is really not achievable without spending a lot more effort and money. Even if I would have performed the tests on a dyno, I would still need to know the variables which go into the dyno itself.
The only thing I can think of to minimize the effect of all the variables is to perform more test, perhaps over a larger time span (like 3rd gear runs from 30-150 kph) and to do more tests with each set. In the end, a greater number of runs would have balanced out more of the unknown variables.
Still, with the results as shown in these tests, the outcome was not so bad at all I think.
Which is that a difference of about 30% in absolute wheel weight will NOT give you a SIGNIFICANT difference in real life acceleration.
Hi Marten,
this is Marinko(rokk) from Germany. we met each other at the Nürburgring. I was there with my 2003 yellow NSX.
Would be intrested to see the results with your new silver NSX-T. You told me, that your old red one was faster than the new one. How much faster is it really? Could you repeat the test.
Regards
rokk
this is Marinko(rokk) from Germany. we met each other at the Nürburgring. I was there with my 2003 yellow NSX.
Would be intrested to see the results with your new silver NSX-T. You told me, that your old red one was faster than the new one. How much faster is it really? Could you repeat the test.
Regards
rokk
you should not get stuck on the acceleration thing. if you want to see a real difference, like others said, install the stock 16/17 setup and then compare. i went from oem 16/17 to oem 17/17 and there was a discernable difference in feedback/suspension feel and small difference in acceleration. since your wheels were both 17/18 setups, you are still rotationally accelerating same size hoops, hence the lighter weight mostly will benefit suspension feedback not acceleration.
what differences did you notice when you went to oem 17/17,ie which setup felt better,and which accelerated better (i'm assuming the smaller wheels were faster),because the oem 17's from 2002+ cars are very light.
i initially installed the oem 17/17 with stock-sized tires. the acceleration was just slightly slower than 16/17 (by an amount you can see while going from used to new tires for example) but front end feel suffered with the biggest drawback was the on-center feel reduction- 16in fronts did have a better feedback. since then i went to 265 rear instead of 255 with non-oem tire brand (conti dw) which definitely slowed the acceleration and killed the front-end feedback. i will go back to oem-size and brand tires after this. these small changes produced (to my perception) such a big difference in feedback that i cannot understand how anyone could justify using 18/19 wheels- imho, you really need to care about looks only or not pay attention to feedback (or use your car for cruzing and 'styling') to justify it.
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No offense, but you use your car solely to race and the few second differences in laps is what counts? I know everyone has their own uses for the NSX, but most people here bought it because it's a beautiful and unique vehicle with substance that performs decently well. Weekend warriors or daily drivers, most people do not track their NSX solely. 18/19s will not deliver ultimate performance, but I didn't know I needed ultimate performance on the streets, especially when a lot of us are barely hitting 300 hp, even after i/h/e.
I agree with the sensation of an unlocked sensation when switching from larger wheels back to stock, but after about 30 minutes of driving, the feeling is loss. The couple tenths of difference can be displaced even by driver error or the difference in environment. I am not arguing the factors of ultimate performance, but rather the application of ultimate performance. The increase of those couple of tenths (if you are consistent enough to realize them) to accleration times are worth the visual appeal of the bigs wheels for most people.
The OEM wheels are light, but they are fairly narrow by todays standards.
While running wider 215/255 or wider-than-OEM 235/275 will improve the handling and outright grip of the car over the narrower 16/17 setup.
0.02
no offense taken but i think you misunderstood the intent- the guy was concerned about acceleration and asked about my experience with swapping oem wheels- if you read my previous post i point out that acceleration variations are negligible, almost, and i consider such as meaningless. furthermore, i am in no way looking to save few tenths on the track (and that is nowhere mentioned) but i do care how my car feels when i drive it (and you don't have to drive on the track to notice the difference) and thats what i was pointing out. i like nice, shiny rims as well but nsx has a very refined feel which is lost completely when going to poorly chosen hardware- there are very few choices out there that still allow you to retain oem feedback and their selection should not be based only on looks. like i said, in my opinion, i see no benefits of sacrificing that feel and feedback for the sake of looks (even if you 'forget' how it 'supposed to feel' after 30 minutes), if thats the case what is the point paying premium for a highly refined product just to destroy its benefits for personal sense of esthetics- once again, my opinion. you do what you like, obviously.
edit: my opinion applies to non-modified car in street-oriented driving. if you start to race then your priorities change- you may sacrifice feedback for outright grip etc. with larger wheels- if you don't race then any mods are purely esthetic.
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Hello Marinko,
Yes, I remember your beautiful NSX very well. If I had seen a yellow NSX before in real life, I might have even bought one myself :smile:
I have not repeated any of the test. Mind you, when I did the test with my new NSX-T, I had only done some very minor modifications.
At that time, my NSX-T weighed about 1360 kg in its lightest form (with a half empty tank) and even 1418 before any modifications and with a full tank.
My old NSX was more like 1340 kg (with a full tank).
Also, my old NSX was stronger and had about 312 HP on the engine (275 RWHP). I am certain that my NSX-T is not as strong. I have a dyno sheet that was done by the previous owner and it states the engine to have 285 HP.
BUT, to give you a comparison, my old NSX did the 20-100 kph run in 2nd gear in about 5.7 seconds, my NSX-T does it in around 6.2 seconds.
In my opinion, that's quite a lot of difference.
Of course, I will do some new testing in the future.
I agree with you on the feel part in a sense, but the sensation of better feeling from aftermarket to stock wheels is only evident when you make the change. That sensation is basically gone after you are riding around with them on for awhile and your mind has adjusted to it. It just like buying a fast car, it feels fast but then you've become use to it until you drive something faster. I mean I have driven vehicles that felt faster than the NSX (with similar, but not equal of course power to weight ratio), but that was because the torque deliver is not as smooth and linear as the NSX. This gave the feeling of a really fast car when in fact it was not that fast.
Butt dyno has always been frowned upon and I think a Butt G meter is just as bad. I will say that nothing feels like driving the NSX, well, nothing I have driven yet, and I have driven many different vehicles. It is very precise and smooth, elegantly balanced. With that said, the change from 18/19 wheels to stock wheels gave the impression that I dropped massive weight but that sensation soon evaporated and real world numbers proved to be minimal like you said. Ride quality was not even that much better, but then again I may have over inflated the tires. I actually prefer the feeling of wider, lower profile tires also. It felt a bit tighter to me but no big difference in overall feeling besides grip. I guess everyone will eventually fall into the compromise of 17/18s and that is what I generally prefer now.
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